CN115118132A

CN115118132A - Driving method and driving module of switching circuit of power converter

Info

Publication number: CN115118132A
Application number: CN202210267980.6A
Authority: CN
Inventors: 许仲杰; 郑元凯; 陈俊江
Original assignee: INFINNO Tech CORP
Current assignee: INFINNO Tech CORP
Priority date: 2021-03-17
Filing date: 2022-03-17
Publication date: 2022-09-27
Also published as: TW202239117A; TWI819528B; US20220352815A1

Abstract

The invention relates to a method for driving a switch circuit of a power converter and a driving module thereof, which can avoid the situation of trough jump and the noise problem caused by trough jump by replacing the original shielding time by additionally generated front shielding time or rear shielding time when the trough of a system is changed.

Description

Switch circuit driving method of power converter and driving module thereof

Technical Field

The present invention relates to a method for driving a switching circuit of a power converter and a driving module thereof, and more particularly, to a method for driving a switching circuit of a power converter capable of operating in a quasi-resonant mode, and a driving module used in the driving method.

Background

Compared with other types of power converters, the switching mode power converter (e.g., flyback power converter) not only has a simpler circuit structure and higher energy conversion efficiency, but also can efficiently provide multiple sets of current outputs. Therefore, the switching power converter is widely used in various products.

The switch-mode power converter such as a flyback power converter can work in a Quasi-Resonant mode (QR), after a previous driving period of the power converter is finished (winding is demagnetized), parasitic oscillation possibly generated by a winding is detected, and a voltage difference between two ends of the switch is smaller at a trough of the parasitic oscillation, so that the switch can be controlled to be conducted at the trough of the parasitic oscillation in the next driving period.

One current implementation is to fix the control switch on detecting the 1 st trough. However, when the load is light, the 1 st trough of the parasitic oscillation appears faster, whereas when the load is heavy, the 1 st trough of the parasitic oscillation appears slower, so that the implementation mode can cause the operation frequency of the system to be higher when the load is light, and the operation frequency to be lower when the load is heavy, which causes the problem of poor power conversion efficiency.

To this end, referring to fig. 1, an improved implementation is to add a masking time Blanking when the system detects the trough of the parasitic oscillation. The length of this Blanking time Blanking may be inversely proportional to the output power of the power converter. As shown in the left side of the drawing, when the load is light, the system output power is not high, so that the shielding time Blanking is long, and the first 3 wave troughs of the parasitic oscillation are all shielded, the system will detect the pulse signal V4 of the 4 th wave trough and control the switch to be actuated at this time. On the contrary, as shown in the right side of the figure, when the load is heavy, the system output power is high, so that the shielding time Blanking is short, only the 1 st wave trough is shielded, and the system will detect the pulse signal V2 of the 2 nd wave trough and control the switch to be actuated at this time. Therefore, the power conversion efficiency can be effectively improved.

In practical applications, however, the conditions such as load may change at any time, which may cause the system to jump or dip (valley jump) in a specific operating state. Referring to fig. 2, the left side of the drawing of fig. 1 is enlarged for illustration. If the length of the Blanking time is close to the time when the 3 rd trough appears, assuming that the system initially detects the pulse signal V4 of the 4 th trough and controls the switch to operate at the same time, when the system first detects the pulse signal V3 of the 3 rd trough due to the load rising and the like and controls the switch to operate, the operating frequency of the system will rise, resulting in the current drop. However, the current drop will advance the time when the 3 rd trough appears, causing the 3 rd trough to easily fall into the shielding time Blanking to be shielded, so the system will be restored to the 4 th trough to control the switch to operate. Therefore, in this operation, the switch must be repeatedly activated at the 3 rd valley and the 4 th valley in turn to balance and output the required output power of the system.

The switching frequency of the above-mentioned jumping wave trough behavior is uncontrollable, and if the switching frequency falls in the audible frequency range of human ears, serious noise is generated, so that manufacturers must additionally perform sound insulation treatment such as glue filling on the power converter, and the volume and the production cost of the power converter are unnecessarily increased. Accordingly, there is a need for an improved method for driving a switch circuit of a power converter.

Disclosure of Invention

An object of the present invention is to provide a method for driving a switching circuit of a power converter and a driving module thereof, which can avoid the occurrence of a trough jump by replacing an original masking time with a pre-masking time or a post-masking time generated additionally when a trough change occurs in a system, thereby effectively avoiding a noise problem caused by the trough jump.

In view of the above, the present invention provides a method for driving a switch circuit of a power converter, which includes calculating a shading time by a driving module according to an output power of the power converter; calculating and generating a front shielding time and a rear shielding time by the driving module according to the shielding time, wherein the length of the front shielding time is shorter than the shielding time, and the length of the rear shielding time is longer than the shielding time; the driving module detects the wave trough change and identifies that the switch circuit is switched at the wave trough, wherein if the wave trough is detected to be switched later, the post-shielding time is selected to replace the shielding time; if the detected wave trough is switched in advance, the front shielding time is selected to replace the shielding time; and detecting a first trough after the shielding time, the rear shielding time or the front shielding time, and controlling the switching of the switch circuit accordingly.

In view of the above, the present invention further provides a driving module, which includes a shielding time calculating unit, wherein the shielding time calculating unit calculates the shielding time according to the output power of the power converter, and calculates and generates the front shielding time and the rear shielding time; and a trough change detecting unit, the trough change detecting unit distinguishes the said switching circuit is switched over in the several troughs, wherein, the trough change detecting unit couples to the calculation unit of the shielding time each other, if detect and delay a trough to be switched over, choose the shielding time after this to replace the shielding time; otherwise, if it is detected that a trough is switched in advance, the front shielding time is selected to replace the shielding time.

Drawings

FIG. 1: a signal diagram of a power converter working in a quasi-resonant mode;

FIG. 2: a signal diagram showing the occurrence of a trough jump phenomenon in a quasi-resonant mode;

FIG. 3: the signal schematic diagram of the embodiment of the switching circuit driving method of the power converter of the invention;

FIG. 4A: the signal diagram of the initial state of the above embodiment;

FIG. 4B: the above embodiment is converted into a signal diagram for detecting the previous trough;

FIG. 4C: the above embodiment is converted into a signal diagram for detecting the next trough;

FIG. 5: a control flow chart of an embodiment of a method for driving a switch circuit of a power converter according to the present invention;

FIG. 6: a schematic diagram of a driving module for implementing the aforementioned embodiment of the switching circuit driving method of the power converter according to the present invention; and

FIG. 7: the circuit architecture of the driving module is schematic.

[ COMPARATIVE EXAMPLES OF DRAWINGS ]

Drive module 1

Shading time calculation unit 2

Output power calculation circuit 21

Shading time calculating circuit 2a

Mask time interval circuit 2b

Wave trough change detecting unit 3

Switching valley detecting circuit 31

Buffer 32

Encoder 33

Buffer unit 4

Trough signal generating unit 5

Zero-cross detection circuit 51

Pulse generating circuit 52

Masking times TB (n), TB (n-1), TB (n +1)

Dead zone times Δ t, Δ t1, Δ t2

Period of resonance T _R

Auxiliary voltage V _AUX

Valley pulse signals V2, V3, V4

Current CS

Feedback voltage VFB

Multiplexer MUX

Switching circuit Switching

Detailed Description

In order to provide a further understanding and appreciation for the structural features and advantages achieved by the present invention, the following detailed description of the presently preferred embodiments is provided:

however, it will be understood by those skilled in the art that various names may be used for different elements, and the description and the claims are not intended to distinguish between elements, but rather are intended to distinguish between elements, components, and techniques. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. Furthermore, the term "coupled" is intended to include any direct or indirect connection that allows two elements to communicate signals or power to each other. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices and other connections.

Hereinafter, the present invention will be described in detail by illustrating various embodiments of the present invention with the aid of the drawings. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein.

The switching circuit driving method of the power converter of the present invention is used to control the switching power converter having the switching circuit, and the switching power converter is, for example, a flyback power converter, etc. capable of operating in the quasi-resonant mode. Referring to fig. 3, the method for driving the switch circuit of the power converter according to the present invention calculates a masking time according to the output power of the power converter. For example, when the system currently detects the nth trough of the parasitic oscillation occurring in the winding (the term "detecting" means that the discrimination switch is switched at the nth trough, the same shall apply hereinafter), the shading time calculated according to the output power at that time can be represented as tb (n). The length of the masking time tb (n) may be inversely proportional to the output power of the power converter, or at least inversely related to the output power, which is not adjusted in this embodiment.

However, in addition to calculating the masking time TB (n), the embodiment of the present invention also calculates a front masking time TB (n-1) and a rear masking time TB (n + 1). The front shielding time TB (n-1) is obtained by subtracting a blind zone time Δ t from the shielding time TB (n), and the rear shielding time TB (n +1) is obtained by adding a blind zone time Δ t to the shielding time TB (n). The dead zone time Δ T can be calculated according to parasitic oscillation of the winding, wherein the parasitic oscillation has a resonant period T _R The dead zone time Deltat is preferably greater than or equal to the resonance period T _R . Although not shown in this embodiment, in other embodiments of the present invention, the masking time TB (n) is subtracted by a first blind areaThe time Δ t1 is used as the front shielding time TB (n-1), and the shielding time TB (n) is added with a second blind zone time Δ t2 to be used as the rear shielding time TB (n +1), and the lengths of the first blind zone time Δ t1 and the second blind zone time Δ t2 may not be equal. However, to ensure better effect, the first dead zone time Δ T1 and the second dead zone time Δ T2 are preferably both greater than or equal to the resonance period T _R 。

Note that in fig. 3, the masking time TB (n), the front masking time TB (n-1), and the rear masking time TB (n +1) are represented by a low potential, i.e. effective at a low potential to mask the parasitic oscillation, and a high potential to represent the end of the masking time without masking the parasitic oscillation, but this is only an example for explaining the embodiment of the present invention, and the signal of the masking time in practical application should depend on the circuit design requirements, and the present invention is not limited thereto.

The following describes how to calculate and use the front shielding time TB (n-1) and the rear shielding time TB (n +1) according to the embodiment of the present invention, please refer to FIG. 4A, when the shielding time is TB (n), the nth-1 trough of the parasitic oscillation is shielded, so the system will detect the nth trough and control the switch to be activated at this time.

Referring to FIG. 4B, the change in conditions such as load may cause the trough to change, for example, when the load is increased, the change may be to the detection of the previous trough (i.e., the (n-1) th trough). Upon detecting this transition, the present embodiment replaces the used masking time TB (n) with the calculated pre-masking time TB (n-1). This is equivalent to the original masking time tb (n) minus a dead zone time Δ t. Therefore, even if the time of the n-1 trough appears is advanced due to the reduction of the current, the time is not easy to be shielded again, so that the system is easy to control the switch to be activated when the system is maintained at the n-1 trough. In other words, the embodiment of the present invention can effectively avoid the occurrence of the trough jump by adjusting the masking time TB (n) to the previous masking time TB (n-1) under the condition. The front shielding time TB (n-1) is shorter than the original shielding time TB (n) by a dead zone time delta T, and the dead zone time delta T can be larger than the resonance period T _R Therefore, the system should be maintained at the n-1 trough easilyIt is relatively easy to control the switch to actuate at the time.

On the contrary, referring to fig. 4C, when the load is decreased, it may be changed to detect the next trough (i.e. the (n +1) th trough). Upon detecting this transition, the present embodiment replaces the used masking time TB (n) with the calculated post-masking time TB (n + 1). This is equivalent to extending the original masking time tb (n) plus a dead zone time Δ t. Therefore, even if the time delay of the nth trough caused by the rising of the current is delayed, the time delay is not easy to exceed the rear shielding time TB (n +1) and is not easy to be detected, so that the system is easy to control the switch to be activated when the nth +1 trough is maintained. In other words, the embodiment of the present invention can effectively avoid the occurrence of the trough jump by adjusting the masking time TB (n) to be the post-masking time TB (n +1) under the condition. Since the post-shielding time TB (n +1) is longer than the original shielding time TB (n) by a dead zone time delta T, the dead zone time delta T can be larger than the resonance period T _R Therefore, it is relatively easy to control the switch to operate when the system is maintained to be easily maintained at the n +1 th trough.

Regardless of whether the front shielding time TB (n-1) or the rear shielding time TB (n +1) is selected to replace the shielding time TB (n), the driving method of the embodiment of the invention preferably adds a buffer time to the action, i.e. the system keeps using the front shielding time TB (n-1) or the rear shielding time TB (n +1) for at least the buffer time. Therefore, due to the fact that the trough jumping is not prone to occur in the buffering time, if the system can achieve balance in the buffering time and output required output power, the system can operate stably, and the noise problem caused by trough jumping can be effectively avoided.

In detail, the output power of the power converter can be simply expressed as follows:

P＝L _P ×I ² ×F

wherein L is _P The inductance (primary inductance) of the primary winding, I the input current (input current), and F the switching frequency (switching frequency) of the switch. Assuming that the system initially detects the nth trough and controls the switch to operate at this time, and then the system changes to detect the nth-1 trough when the load rises, the output power before and after the changePcrritical 1 and Pcrritical 2 can be expressed as simplified formulas:

Pcritical1＝L _P ×I _max ² ×F _min，n

Pcritical2＝L _P ×I _max ² ×E _max，n-1

if the system does not execute the driving method of the embodiment of the invention, after the conversion, if the output power exceeds the requirement of the load, the system can feed back the correction to reduce the current and increase the switching frequency, so that the nth trough is detected again, and the situation of repeatedly jumping troughs is formed to balance the output power.

Once the driving method of the embodiment of the present invention is executed, the pre-masking time TB (n-1) can be selected to avoid the trough jump, and the pre-masking time TB (n-1) can be maintained at least for the buffering time, so that although the system still feeds back the correction to reduce the current and increase the switching frequency during the buffering time, once the following formula is satisfied, the system can reach the balance and output the required output power during the buffering time without detecting the nth trough again. Wherein, the Pmean of the following formula is the required output power, and a is the parameter of the system feedback correction.

Accordingly, the above-mentioned embodiment of the method for driving the switch circuit of the power converter according to the present invention can arrange the control flow chart shown in fig. 5, which is described as follows:

and (3) calculating the shielding time: calculating a shielding time TB (n) according to the output power of the power converter, subtracting a blind zone time from the shielding time TB (n) to generate a front shielding time TB (n-1), and adding a blind zone time to the shielding time TB (n) to generate a rear shielding time TB (n + 1).

Blind area time calculation: calculating the dead zone time required for the calculation of the shielding time, wherein the dead zone time Deltat is preferably greater than or equal to the resonance period T of the parasitic oscillation generated by the winding _R So according to the resonant period T _R Can define proper blind areaThe length of time. Notably, the resonance period T _R The calculation can be actually performed according to the parasitic oscillation signal of the winding; alternatively, the resonant period T may be for the same system as the resonant period T, since the parasitic oscillations are caused by the inductance and parasitic capacitance of the winding (e.g., parasitic capacitance of the switch) _R May be substantially constant, so that the resonant period T can be obtained by pre-measuring and temporarily storing the result _R And the dead zone time can be preset without necessarily calculating the resonance period T in real time _R 。

Detecting wave trough transformation: when the system operates in a quasi-resonance mode, if the system initially detects the nth trough, the trough-changing detection system detects whether the nth trough is still detected (not changed); or whether the (n +1) th trough is detected (the latter trough is detected and changed); or whether the (n-1) th trough is detected (a transition occurs and the previous trough is detected).

Selecting a post-shading time: when the valley transition is detected and the n +1 th valley is detected, the post-masking time TB (n +1) is selected to replace the original masking time TB (n).

Selecting a pre-shading time: when the valley change is detected and the (n-1) th valley is detected, the previous masking time TB (n-1) is selected to replace the original masking time TB (n).

Buffer time addition: the system is allowed to maintain the pre-mask time TB (n-1) or the post-mask time TB (n +1) for at least a buffer time, so as to try to allow the system to reach the balance and output the required output power within the buffer time without detecting the nth trough again.

Referring to fig. 6, a driving module 1 for implementing the embodiment of the switching circuit driving method of the power converter of the present invention is disclosed. The driving module 1 includes a shading time calculating unit 2, a trough change detecting unit 3, a buffer unit 4, and a trough signal generating unit 5.

The shielding time calculating unit 2 calculates a shielding time TB (n) according to the output power of the power converter, subtracts a dead zone time from the shielding time TB (n) to generate a previous shielding time TB (n-1), and then calculates a current shielding time TB (n-1) according to the output power of the power converterThe masking time TB (n) is added with a dead zone time to generate a post-masking time TB (n + 1). The masking time calculating unit 2 may include an output power calculating circuit 21, and the output power calculating circuit 21 may calculate the output power of the power converter according to the information such as the current CS of the primary winding, the winding discharge time, or the error feedback voltage VFB of the secondary winding, but the present invention is not limited to the method for obtaining the output power information, and the output power calculating circuit 21 may be omitted if the system has the output power information in a specific application. In addition, the shielding time calculating unit 2 can receive the voltage signal of the winding, which is generally obtained by providing an auxiliary winding (as shown in the figure), so that the obtained auxiliary voltage V is actually the auxiliary voltage V induced on the auxiliary winding _AUX . The auxiliary voltage V _AUX For calculating the resonant period T of the parasitic oscillation occurring in the winding _R . The resonant period T, as described above _R Or dead zone time may be measured in advance and stored in the buffer.

The trough-change detecting unit 3 uses whether the detected system still keeps detecting the nth trough (no change occurs); or whether the (n +1) th trough is detected (the latter trough is detected and changed); or whether the (n-1) th trough is detected (a transition occurs and the previous trough is detected).

The valley change detecting unit 3 is coupled to the buffering unit 4, and the buffering unit 4 is provided for adding a buffering time. The masking time calculating unit 2 and the buffering unit 4 are coupled to a multiplexer MUX. Therefore, when the valley change detection unit 3 detects the valley change and detects the (n +1) th valley, the multiplexer MUX can be controlled to select the post-masking time TB (n +1) and maintain the buffering time; when the valley transition detection unit 3 detects a valley transition and detects the (n-1) th valley, the multiplexer MUX is controlled to select the front shielding time TB (n-1) and maintain the buffering time.

The valley signal generating unit 5 generates the auxiliary voltage V according to the voltage signal of the winding (in the present embodiment) _AUX ) To generate the pulse signal of each wave trough, and to make the pulse signals and the shielding time outputted by the multiplexer MUXThe first AND gate is also transmitted to an AND gate (AND gate), thereby detecting what the first valley is after the masking time, AND controlling the switch to turn on at the valley.

Fig. 7 demonstrates one of the circuit architectures that actually constitute the driver module 1. The output power calculating circuit 21(Load calculating circuit) of the masking time calculating unit 2 may be a multiplier, an integrator, or the like, depending on the signal according to which the calculated power is calculated. The masking Time calculating unit 2 may be further divided into a masking Time calculating circuit 2a (masking Time calculating) and a masking Time separating circuit 2b (masking Time separating). The masking time calculation circuit 2a is used to calculate a masking time tb (n) that is inversely proportional or inversely related to the output power. The shielding time division circuit 2b can be based on the auxiliary voltage V _AUX Calculating the resonant period T of the parasitic oscillation _R And further define a dead zone time. However, the resonant period T _R Or dead zone time may be measured in advance and stored in the buffer. The shielding time division circuit 2b is further used for subtracting a blind zone time from the shielding time TB (n) to generate a front shielding time TB (n-1), and adding a blind zone time to the shielding time TB (n) to generate a rear shielding time TB (n + 1).

The Valley change detection unit 3 can be completed by simple circuits such as a switching Valley detection circuit 31(Valley Now), a register 32, an encoder 33, etc., the switching Valley detection circuit 31 can include circuits such as a counter, etc., which can be based on the auxiliary voltage V _AUX The calculation control switch Switching is switched at the trough. Further, once it is detected that the switched trough of the control switch is changed, the value of the register 32 will not be equal to that of the switched trough detecting circuit 31, and the subtraction result can determine whether the system detects the next wave or the previous trough.

The buffer unit 4 may include a frequency generation circuit, a delay circuit, and the like for adding a buffering time.

The valley signal generating unit 5 may include a Zero-crossing detecting circuit 51 (ZCD Logic) and a Pulse generating circuit 52(Pulse), and the auxiliary voltage V may be applied _AUX By a certain threshold value, e.g. zeroSo as to generate a pulse signal. Therefore, the pulse signals indicating each trough can be generated, so that the pulse signals and the shielding time output by the multiplexer MUX can be used for detecting the first trough after the shielding time, and the pulse signals and the shielding time output by the multiplexer MUX can be used for controlling the switch to be switched on at the trough.

By implementing the switching circuit driving method of the power converter or the driving module thereof in the embodiment of the invention, when the system has a trough change, because the additionally generated front shielding time TB (n-1) or rear shielding time TB (n +1) is selected in the buffering time, the trough jump can be avoided, if the system can reach balance in the buffering time and output the required output power, the system can stably operate to effectively avoid the noise problem caused by trough jump, and compared with the prior art, the volume and the production cost of the power converter can be reduced.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not intended to limit the scope of the present invention, which is defined by the appended claims.

Claims

1. A method for driving a switch circuit of a power converter is performed by a driving module, and the method includes:

calculating a shielding time by the driving module according to the output power of the power converter;

calculating and generating a front shielding time and a rear shielding time by the driving module according to the shielding time, wherein the length of the front shielding time is shorter than the shielding time, and the length of the rear shielding time is longer than the shielding time;

the driving module detects the wave trough change and identifies that the switch circuit is switched at the wave trough, wherein if the wave trough is detected to be switched later, the post-shielding time is selected to replace the shielding time; otherwise, if it is detected that a trough is switched in advance, the front shielding time is selected to replace the shielding time; and

detecting the first trough after the shielding time, the rear shielding time or the front shielding time, and controlling the switching of the switch circuit accordingly.

2. The method as claimed in claim 1, wherein the use of the rear masking time or the front masking time is maintained for at least a buffering time after the masking time is replaced with the rear masking time or the front masking time.

3. The method as claimed in claim 1, wherein the front shielding time is obtained by subtracting a first dead zone time from the shielding time, and the rear shielding time is obtained by adding a second dead zone time to the shielding time.

4. The method as claimed in claim 3, wherein the first dead zone time is equal to the second dead zone time.

5. The method as claimed in claim 3, wherein a parasitic oscillation exists in a winding coupled to the switching circuit, the parasitic oscillation has a resonant period, and the first dead zone time and the second dead zone time are greater than or equal to the resonant period.

6. The method of claim 5, further comprising calculating the resonant period according to the parasitic oscillation signal.

7. A driver module, coupled to a switching circuit of a power converter, comprising:

a shielding time calculating unit, which calculates a shielding time according to the output power of the power converter and generates a front shielding time and a rear shielding time according to the shielding time; and

a trough change detection unit, which identifies that the switch circuit is switched at the second trough, wherein the trough change detection unit is coupled with the shielding time calculation unit, if detecting that a subsequent trough is switched, the subsequent shielding time is selected to replace the shielding time; otherwise, if it is detected that a trough is switched in advance, the front shielding time is selected to replace the shielding time.

8. The driving module as claimed in claim 7, wherein the valley change detecting unit and the masking time calculating unit are respectively coupled to a multiplexer, and the multiplexer selects one of the masking time, the post-masking time or the pre-masking time for output according to the detection result of the valley change detecting unit.

9. The driving module as claimed in claim 7, further comprising a buffer unit coupled to the valley change detection unit, wherein the masking time calculation unit and the buffer unit are respectively coupled to a multiplexer for controlling the multiplexer to select one of the masking time, the post-masking time or the pre-masking time for output according to the detection result of the valley change detection unit and maintain a buffer time.

10. The driving module according to claim 8 or 9, further comprising a valley signal generating unit, wherein the winding coupled to the switching circuit has parasitic oscillation, the valley signal generating unit generates a pulse signal for each valley according to the signal of the winding, and the driving module detects a first valley after the masking time, the rear masking time or the front masking time according to the pulse signal and the output of the multiplexer, and controls the switching of the switching circuit accordingly.

11. The driving module of claim 7, wherein the mask time calculating unit subtracts a first dead zone time from the mask time to obtain the front mask time, and adds a second dead zone time to the mask time to obtain the rear mask time.

12. The drive module of claim 11, wherein the first dead zone time is equal to the second dead zone time.

13. The driver module as claimed in claim 11, wherein the winding coupled to the switching circuit has a parasitic oscillation, the parasitic oscillation has a resonant period, and the first dead time and the second dead time are greater than or equal to the resonant period.

14. The driving module as claimed in claim 13, wherein the shading time calculating unit calculates the resonant period according to the signal of the parasitic oscillation.

15. The driving module of claim 11, wherein the shading time calculating unit comprises an output power calculating circuit, and the output power calculating circuit calculates the output power of the power converter.